1. Field of the Invention
This invention relates to a dithiolate metal complex compound usable as a dye component in an optical information recording medium, a production method of the complex compound, and an optical information recording medium comprising a polymethine dye and the complex compound.
2. Discussion of Background
Recently, a thin film containing as its main component an organic dye having both light-absorptivity and light-reflectivity, such as a cyanine dye, a triaryl methane dye, a mercocyanine dye, a naphthoquinone dye, a xanthene dye or a squalyrium dye, has been proposed as a recording layer for use in an optical information recording medium, for example, in Japanese Laid-Open Patent Applications 51-135886, 57-11090 and 61-70503.
The conventional recording layer made of a metallic thin film is now being substituted by a recording layer made of the above organic thin film. A thin film containing the organic dye has a low melting point and decomposition point, and also has low thermal conductivity, so that a recording layer made of such an organic thin film has high sensitivity, allowing information to be recorded in this layer with high density.
In addition to the above-mentioned advantages, the thin film containing the organic dye can be simply formed by a coating method, so that it can be produced with higher productivity and lower production cost.
The thin film containing the organic dye, however, cannot stand for a long term because the organic dye tends to lose its color when natural light or a reproduction laser beam is repeatedly applied to the film. Moreover, when the thin film is formed by a coating method, a halogenated hydrocarbon or the like is used as a solvent, so that limitations are placed on resins which can be used as a substrate.
In order to overcome the above shortcomings, intensive studies are now being carried out both on dyes which are highly stable in natural light in the red to near-infrared region, as well as in a reproduction light, and on stabilizing agents which will effectively improve the stability in the light.